Programmable logic devices, such as field programmable gate arrays (FPGAs), typically radiate electromagnetic noise during operation. Noise generated by digital circuitry in an FPGA can hamper the operation of nearby analog circuitry. For example, noise generated by an FPGA can unintentionally be amplified by an analog audio amplifier die that is mounted on the same printed circuit board.
FIG. 1 (prior art) illustrates an analog application of an FPGA involving a cell phone. FIG. 1 is a simplified cross-sectional diagram of an FPGA die 10 in an integrated circuit package 11 disposed on a printed circuit board 12. An analog audio amplifier die 13 is mounted separately on the printed circuit board 12.
Radio frequency (RF) signals 14 are received by an antenna 15 and converted to intermediate frequency (IF) signals 16 by RF circuitry 17. The IF signals 16 are then communicated to FPGA die 10 through a trace 18 on printed circuit board 12 and through a bond wire 19 between package 11 and FPGA die 10. To simplify the diagram, the lid of package 11 is not shown in FIG. 1.
IF signals 16 are digitized, and then digital signal processing is performed by DSP circuitry 20 on FPGA die 10. Audio signal processing is then performed by audio control circuitry 21 and audio synthesis circuitry 22 in FPGA die 10. The resulting audio signals are then communicated from FPGA die 10 to audio amplifier die 13 through a bond wire 23, a trace 24 on printed circuit board 12 and through a bond wire 25 between audio amplifier die 13 and its package 26. Audio amplifier die 13 drives a speaker 27.
FPGA 10 contains circuitry, such as DSP circuitry 20, that operates using high frequency signals and exhibits fast switching transients. Circuitry in FPGA 10 therefore typically emits substantial electromagnetic radiation in the audio frequency range. FPGA 10 also draws surges of current from power/ground supply 28. This results in the power and ground supplied to the FPGA 10 to include noise. If audio amplifier die 13 were powered directly by power/ground supply 28, then audio amplifier die 13 may pick up some of this noise. To combat this problem, audio amplifier die 13 is powered by separate, isolated analog power and ground signals 29. An analog power regulator 30 regulates power/ground supply 28 and outputs analog power and ground signals 29. A separate logic power regulator 31 is also coupled to power/ground supply 28 and outputs the ground and Vcc signals that power the digital circuitry in FPGA die 10. Voltage regulators 30 and 31 are typically disposed on printed circuit board 12.
The analog application of FPGA die 10 shown in FIG. 1 employs considerable printed circuit board space. Moreover, power is consumed as signals are driven from FPGA die 10 to audio amplifier die 13 through bond wire 23, physically-large trace 24 and bond wire 25.
A more compact and lower-power solution is desired.